During the continuous casting of steel, for example, molten metal is transferred from large ladles into intermediate pouring vessels called tundishes. From these tundishes, the molten metal is poured into ingots, or other molds, to cast the molten metal.
While in the tundishes, impurities (called "inclusions") in the molten metal float to the top, forming a "slag" layer of impurities, and the pure, substantially "inclusion-free" metal exits from the bottom. Depending on the size of the tundish, and the flow rate of molten metal, the molten metal may not always have enough residence time in the tundish to permit the impurities to float to the top. To increase the residence time in tundishes, and regulate the flow of molten metal, baffles having flow control openings have been developed. One such baffle is disclosed in U.S. Pat. No. 4,667,939, issued to Luyckx.
Impurities entrained in the molten metal may affect the final cast product. Processing of the metal may be thereby hampered, or the finished product may be less pure, less structurally sound or have poor finishing quality. These impurities originate from several sources. For example, impurities may include metallic impurities such as alkaline and/or alkaline earth metals, dissolved entrained gases and occluded tundish surface oxide films which have broken up in the molten metal. In addition, inclusions may originate from non-metallic sources such as carbides or borides and eroded furnace and trough refractories. Effective removal of these impurities, with the aid of apertured baffles and other flow control devices, as appropriate, is an important aspect of molten metal processing.
As described in the above-referenced U.S. Pat. No. 4,667,939, tundish baffle openings or apertures are typically round. The apertures may be formed straight through the tundish baffle in a horizontal orientation, or may be slanted at an angle to direct the molten metal (and inclusions) somewhat upward. Also, the apertures may be cylindrical or frustoconical (i.e. tapered).
One of the problems existing in prior art apertured tundish baffles is that non-metallic inclusions tend to collect or "cake" around the outer circumferences of the round apertures. As this occurs, the baffle openings gradually become smaller until the flow of molten metal through the openings is blocked or choked off. Even when the round openings are only partially blocked, the functions of the apertured baffles are inhibited because the openings no longer control the residence time and flow of molten metal in the desired manner. Therefore, there is a need or desire in the iron and steel industry for apertured baffles which can accommodate the buildup of non-metallic inclusions in the apertures without seriously disrupting the residence time and flow control functions of the baffles.